A timepiece movement is generally secured by the cooperation between a bottom plate of the movement and a middle part or casing ring of the timepiece case, via two or three flanges, depending upon the size of the movement. These flanges are flat or folded and a securing screw holds each flange by friction. This securing method is not perfect, firstly because it does not provide any centring, particularly angular centring, and also because it is very sensitive to shocks and accelerations, which may cause some movements to move angularly, until they become detached from their case in the event of a shock, and are then only secured by the stem, which results in misaligned components and wear. Simply tightening the securing screws is sufficient to angularly move the movement.
The defects caused in this manner are unacceptable in many timepieces, and more specifically in those which have additional functions controlled by push-buttons, such as chronographs. The push force transmitted to the push-buttons by the user is often significant, and if the geometry is wrong, the push-buttons and associated mechanisms are subjected to additional stresses and thus high wear. This is particularly the case for a single chronograph button which is sensitive to this type of geometrical defect.
Keeping the movement and case firmly secured is a gauge of longevity and the problem is therefore serious. Curiously, few solutions have been provided to this problem. Most are based on holding the movement resiliently in the case, as in CH Patent No. 482 238 in the name of Claude Baillod, which has an elastic annular element at the periphery of the case, or in EP Patent No. 1 970 779, in the name of Richemont, where a gasket centres the movement when it is compressed while being fitted into the case, or EP Patent Application No. 2, 275 882, in the name of ETA SA which has an annular part pushing a casing ring onto the middle part. Precise centring solutions have been proposed, particularly by CH Patent No. 160 803 in the name of Aegler Rolex, with a cam used for centring, but with plane-plane friction which is therefore liable to be displaced in the event of a shock. CH Patent No 229 462 in the name of Henri Collomb and Tavannes Watch proposed a centring and holding method using a ring spring which rests on the inner wall of the case, working in friction. CH Patent No. 229 232 by the same Applicants discloses holding the movement via a spring. CH Patent No. 265 254 in the name of Henri Collomb proposes centring the movement by a force fitted flange. These different designs have not properly resolved the problem of resistance to shocks during use and the problem remains to this day. DE Patent No. 17 03 377 U in the name of JUNGHANS discloses a flange abutment between a bottom plate and a washer which itself rests on the middle part. The corresponding bearing surfaces are flat which in unfavourable for proper centring.
CH Patent Application No. 619 345 in the name of PERRET FRERES discloses a peripheral gasket, with a C-shaped section, between a superposed back cover and middle part, and a casing ring carrying a movement and comprising lugs which project radially through apertures arranged in the peripheral gasket.
GB Patent Application No. 2 022 877 A in the name of SUWA SEIKOSHA discloses a flange holding a movement relative to a middle part wherein the flange is in an oblique wedged position.
U.S. patent application Ser. No. 865 656 A in the name of PORTER WILSON discloses a configuration with a flange spring and alternating supports on the flange and middle part.